ABSTRACT Activation of immune cells is a key process in the initiation and progression of neurodegenerative diseases, particularly multiple sclerosis (MS). Presently, there is no non-invasive imaging method that can specifically detect activated immune cells and neuroinflammation in clinical settings. Recent development of radiotracers for positron emission tomography (PET) have shown great potential for the detection of cells from the adaptive immune system. Specifically, 2'-deoxy-2'-[18F]fluoro-9-?-D- arabinofuranosylguanine ([18F]F-AraG) has been shown to enable the detection of activated primary T-cells in graft-versus-host disease. At the same time, hyperpolarized 13C magnetic resonance spectroscopic imaging (HP 13C MRSI) is emerging as a new metabolic MR method to monitor enzymatic reactions in vivo in real-time. HP [1-13C] pyruvate has proven to be sensitive to highly glycolytic pro-inflammatory cells from the innate immune system (i.e. Macrophages) in animal models of peripheral inflammation, MS and traumatic brain injury. Importantly, both [18F]F-AraG and HP [1-13C] pyruvate have shown great promise in first-in-human studies of cancer. In this project, we propose to investigate the potential of HP [1-13C] pyruvate and [18F]F-AraG PET imaging to non-invasively assess cerebral lesion stage and to monitor response to immunomodulatory therapies in a novel murine model for MS. To do so, HP 13C MRSI and PET imaging sessions will be performed at key time points during disease induction and progression. Next, HP [1-13C] pyruvate and [18F]F-AraG will be used to evaluate treatment response from two clinically relevant and commonly prescribed drugs for MS, Dimethyl-fumarate and Fingolimod. PET and MRI findings will be confirmed using ex vivo correlates of tracer biodistribution and immuno-histopathological markers for inflammation and lesion characterization. Because HP [1-13C] pyruvate and [18F]F-AraG PET are readily available for clinical translation, drugs and the imaging findings, outcomes from this project will identify clinically relevant biomarkers that could provide diagnostic, prognostic and therapeutic information to better achieve precision medicine for patients with MS. Upon clinical translation, such methods could help refine therapeutic regimens and lead to better clinical outcomes and patient quality of life.